1. Technical Field
The present invention relates to improvements in skid assemblies employed to permit inspection and maintenance equipment to slide freely when pulled or otherwise driven through pipelines. Although the preferred embodiment of the present invention is described in connection with a packer apparatus used for detecting and sealing leaks in sewer lines, it is to be understood that the present invention has broader applicability and may be employed with a wide variety of equipment utilized in various types of pipelines.
2. Discussion of the Prior Art
Packer assemblies are commonly employed to detect and/or seal leaks in sewer lines. Such assemblies are generally cylindrical with a diameter smaller than the internal diameter of the pipe in which the assembly is to be used. A pair of axially spaced sleeves are inflatable on the packer assembly to seal off a section of a pipe therebetween so that pressurized liquid can be delivered to the sealed space. Such packers are typically provided with skid assemblies at their opposite ends to facilitate smooth movement of the packer to the desired location within the pipe. Each skid assembly typically includes four skid blades spaced equiangularly about the central longitudinal axis of the packer and extending radially beyond the packer periphery so that only the edge of the skid blade, and not the packer itself, rests upon and contacts the internal pipe surface. The angular spacing assures that at least two of the skid blades of each assembly ride along the internal pipe surface as the packer is transported through the pipe.
A typical prior art packer assembly of the type described above is illustrated in FIG. 1 to which specific reference is now made. The packer assembly includes a generally cylindrical body 10 having annular end plates 11 and 12. Such packers are well known, and typical examples are found in U.S. Pat. Nos. 3,618,639, 3,103,235 and 3,834,421. Secured to each end plate 11, 12 are four substantially identical skid blades 13, only three of which are visible for each end plate in FIG. 1. The four skid blades 13 comprising each skid assembly are spaced at equal angles of 90 degrees about the central longitudinal axis X--X of the packer body 10. The outer edge of each blade 13 extends in a straight line from the end plate 11 or 12 axially outward and radially outward from the packer to an apex 14. From apex 14 the outer edge extends convexly in directions axially away from the packer body 10 but radially inward to intersect the blade inner edge 15. The latter extends back to the end plate 11 or 12 in a 20 direction generally parallel to the axis X--X.
The four identical skid blades 13 extending from end plate 11 all have their apices 14 disposed in a common plane Y.sub.1 --Y.sub.1 oriented perpendicular to axis X--X. Likewise, the apices 14 of the four identical skid blades extending from end plate 12 are all disposed in a common plane Y.sub.2 --Y.sub.2 oriented perpendicular to axis X--X. This arrangement has the disadvantage of preventing the packer assembly from moving through radial offsets that may occur at the intersections of pipe sections in a pipeline. More specifically, and referring to FIG. 2 of the accompanying drawings, two adjacent pipe sections 16 and 17 are shown radially offset, a situation that might occur due to the ground settling, etc. Packer 10, with its end plate 11 and associated skid assembly, is shown approaching the offset junction between pipe sections 16 and 17. In the illustrated example, the spacing between the apices 14 of diametrically opposite skid blades is shown approximately equal to the internal diameter of the pipe section in order to emphasis the inability of the skid assembly to traverse the offset pipe junction. Specifically, the offset junction has an effective internal diameter that is smaller than the space between diametrically opposite blade apices 14 and, therefore, blocks passage of the packer into pipe section 16. Typically, the spacing between apices of diametrically opposite skid blades is somewhat less than the internal pipe diameter. For example, with a pipe section having an eight inch internal diameter, the distance between diametrically opposite skid blade apices might typically be seven and one-half inches. If the radial offset between pipe sections 16 and 17 is greater than one-half inch, the skid assembly will not fit through the offset junction because the opening at the junction will be less than the seven and one-half inch spacing between diametrically opposite skid blade apices 14. Reducing the radial dimension of the skid blade apices could mitigate the problem; however, such reduction would subject the inflatable packer sleeves to abrasive damage due to contact with the internal pipe wall and projections therefrom as the packer is transported through the pipeline.